Within induction and other electrical motors, vibration of the motor shafts may be measured and monitored to identify conditions that may be indicative of impending machine failure or the need for machine maintenance. For example, vibration of the rotor shaft may be measured, and if the vibration level is found to be above a predetermined threshold level, the detection system may signal a warning or initiate a follow-up action. The threshold level may be a peak-to-peak measurement value. For example, it is commonplace to use one or more non-contacting, eddy current proximity sensors to monitor such vibration levels. The one or more eddy current sensors may be positioned proximate to a suitable location on the rotor shaft, such as at a bearing journal or on another surface portion of the rotatable rotor shaft. The peak-to-peak runout value may be displayed on a suitable display, such as an oscilloscope or other device.
Runout measured by the eddy current sensor is, in actuality, a combined measurement of mechanical runout and electrical runout (hereinafter “combined runout”). Mechanical runout is the deviation in the mechanical dimension about the rotor shaft at the measurement surface. In particular, mechanical runout is generally limited to relatively-close tolerances during she machine shaft machining process, e.g., during lathe turning and/or grinding operations. Certain contributors to mechanical runout, such as shaft diameter, shaft roundness (e.g., circularity), and surface finish are generally met after the initial machining process is completed. However, even though rotor shaft mechanical runout readings, e.g., via dial indicator, profilometer, etc. may be within acceptable tolerances, the electrical runout due to material anomalies, material permeability variations, material resistivity, and/or other factors may provide a combined runout measured via the eddy current proximity sensor that may be outside of a desired tolerance level. Such tolerance levels may be set by certain runout standards, such as API 541, 4th edition. In such instances, prior methods have attempted to re-work the shaft surface in an attempt to further reduce the combined runout measured by the eddy current proximity sensor.
However, existing methods for re-work of shaft surfaces (e.g., measurement surfaces such as shaft journals) tend to be complicated and take a substantial amount of time. Moreover, in some instances they may change the surface finish (e.g., roughness) appreciably or otherwise affect shaft dimensions. Thus, improved shaft re-work methods that are both efficient and cost effective and do not appreciably affect shaft dimensions are sought.